According to one reference, the optimal film thicknesses of Pt and Pd at which the anisotropy magnetic field is at a maximum are about 0.2 nm and 0.6 nm, respectively, for multilayer films of Co/Pt and Co/Pd. J. Applied Physics 97, 10J109 (2005). According to another reference, as the film thickness of Pd in the multilayer film of Co/Pd becomes greater, the discharge gas pressure in forming the multilayer film and the anisotropy energy for each (Co/Pd) layer increases. IEEE Transaction on Magnetics, Vol. 39, No. 5, pp. 2714-2716, September 2003.
Japanese Patent Office (JPO) Pub. No. JP-A-5-28552 proposes a method for manufacturing a magneto optical recording medium having an artificial lattice film in which a first layer made of a metal selected from Co, Fe and Co—Fe alloy, and a second layer made of a metal selected from Pt, Pd and Pt—Pd alloy are laminated repeatedly as a recording layer.
US Pat. App. No. US2006/0154110A1 discloses a method exemplary of thermal assisted recording. US Pat. App. No. US2002/0101673A1 discloses a method for local heating of a medium, such as by using a near field heater. Also, as disclosed in JPO Pub. No. JP-A-5-20635, a magnetic head having a thin film magnetic head element is formed with a thin film resistor in which the tip of a magnetic pole is thermally expanded to project by turning on electricity to generate heat, as needed, or a thin film resistor in which the tip of the magnetic pole is thermally expanded to project by turning on electricity to generate heat when the magnetic head performs the reading/writing from/to a magnetic disk. The thin film resistor is formed inside an insulator layer of a thin film magnetic head element to have a smaller gap with the magnetic disk surface due to the projecting tip of the magnetic pole. JPO Pub. No. JP-A-2007-128573 proposes a head for a thermal assisted recording device in which the magnetic pole is disposed on top of a scatterer for generating a near field light on the bottom of a slider.
Generally, the head is loaded from an unloaded storage state away from the disk onto a rotating disk from the outer circumferential side. The head generally seeks from the inner circumference to a specific radius on the outer circumference without anchoring for a long time. If the head is kept flying in the limited specific radius continuously for a long time, a lubricating layer formed on a cap layer is depleted, causing the cap layer to easily break, and possibly leading to a device crash and failure. For example, if the head is kept flying on a medium having a radius of 32.5 nm in the limited specific radius of 21 nm at a peripheral speed of 11.88 m/s, the sliding reliability is lower only in an area near this radius of 21 nm. While the medium using the Co/Pd artificial lattice has a higher signal-to-noise-ratio (SNR) than the medium using the Co/Pt artificial lattice, it is degraded in the continuous anti-sliding reliability of measuring the reproduction output for 4096 seconds at 70° C. in which the head flying amount is set from 1.5 nm to 2 nm with the head fixed in the same radius. A thermal energy assisted medium using the artificial lattice having a high SNR that is also excellent in anti-sliding reliability has not been heretofore discovered.
Therefore, it would be beneficial in order to receive all benefits from a thermal assisted recording medium to have a medium which has an excellent continuous anti-sliding reliability during low-flying of the head, but still has a high SNR.